The present invention relates generally to multiple piece fasteners and more particularly to two piece fasteners of the type comprising a pin and swageable collar designed for installation by a pulling tool which exerts a pulling force on the pin and reaction force on the collar so as to swage the collar into engagement with the pin.
Conventional pull-type two piece fasteners include a pin and a collar adapted to be swaged thereon. The pin has an elongated shank provided with a head at one end, a plurality of lock grooves and a plurality of pull grooves defined by substantially uniform diameter crests alternating with valleys of substantially uniform diameter. These pull grooves are provided on a separable pintail portion of the shank. The collar is applied to the shank of the pin subsequent to insertion of the pin into a prepared opening in workpieces to be joined. An installation tool having a jaw assembly is applied to the pin with the jaws of the installation tool having a plurality of teeth adapted to engage a selected number of the pull grooves whereby a pulling force can be exerted on the pin. The installation tool also has a swaging anvil adapted to engage the collar and to swage the collar into engagement with locking grooves on the shank portion of the pin in reaction to the pulling force. As the pulling force continues to increase in magnitude the pintail portion of the shank is separated at a breakneck groove provided on the pin shank between the locking grooves and the pull grooves. The pintail portion is discarded and the setting operation is complete. This pintail portion, however, represents a cost factor in the fastener which contributes nothing to the fastened joint as it serves only to aid in the installation of the fastener.
Typically these pintail portions have been fabricated with a substantially greater number of pull grooves than that required to properly set the fastener. One of the reasons for this excess number of pull grooves and hence extra length of the pintail is to ensure that a sufficient number of pull grooves are engaged by the jaws of the installation tool to develop the pull force required to set the fastener. If an insufficient number of pull grooves are engaged by the jaws, the engaged pull grooves may be stripped before complete setting of the fastener thus requiring removal of the partially installed fastener and installation of a new fastener.
While present material costs attributable to this lengthy pintail when such pull-type fasteners are fabricated from low cost materials may not be significant enough to generate much concern, this is not necessarily the case when the fasteners are fabricated from more costly, exotic metals such as titanium which are commonly used in the aerospace industry. In the latter case, it is very desirable to reduce to an absolute minimum the amount of material required and hence the costs associated with the fastener and particularly to reduce the amount of that material and associated cost which does not contribute to the integrity or strength of the fastener as installed i.e. the disposable pintail. One problem, however, is to assure that the minimum number of grooves are engaged by the tool jaws to preclude stripping.
Accordingly, the present invention provides a fastener and associated installation tool jaw assembly by which the amount of disposable pintail material is minimized. In a preferred form of the invention, the pintail portion of the pin is reduced to a minimum length required to provide only that number of pull grooves necessary to provide sufficient strength to accept the setting force to be exerted thereon by the installation tool when all of the grooves are engaged. In a different form of the invention, the pintail portion is totally eliminated, the pull grooves being provided within an axially inwardly extending opening provided in the pin portion of the fastener. In both of these embodiments, the pull grooves are designed to cooperate with the jaws of the installation tool in such a manner as to preclude engagement of less than the minimum number of pull grooves required before any pulling force can be generated thereby eliminating the possibility of stripping of the grooves.
Thus, the present invention provides a pull-type fastener and associated installation tool jaw structure which enables the length of the pintail to be substantially reduced or even eliminated while still precluding the possibility of stripping the fastener. The reduced length or complete elimination of the pintail portion affords the advantage of cost savings which can be significant where costly materials are employed.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.